The present invention relates to a fibrous zeolite and a preparation method thereof, and more particularly, to a fibrous zeolite which is easy to use as a functional material, can be easily adsorbed and desorbed when used as a catalyst, and can be directly used as a reinforcement material and preparation method thereof.
Scientific and industrial research into zeolite has been very active in the catalyst field since the discovery of stilbite, a natural zeolite. Currently, 34 kinds of natural zeolites are known, however industrial use thereof is limited due to pore size, crystalline structure and purity. Therefore, a powdered zeolite is synthesized and widely used as a detergent, a catalyst, an adsorbent and a moisture absorbent.
A natural or synthetic powdered zeolite can be used as a catalyst for conversion reactions of many kinds of hydrocarbons. Also, since a powdered zeolite can selectively adsorb molecules which have a predetermined form and size due to its uniform pore structure, it is called as a molecular sieve.
Several types of synthetic powdered zeolites are prepared using various methods of synthesis. Different kinds of synthetic zeolite with variable ratios of SiO.sub.2 /Al.sub.2 O.sub.3 as a main component include zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), and ZSM-5 (U.S. Pat. No. 3,702,886).
As another kind of synthetic zeolite, U.S. Pat. No. 4,410,501 discloses a titanium-silicalite (hereinafter, referred to as TS-1) which substitutes titanium oxide for aluminum oxide in the conventional zeolite composed of aluminum oxide and silicon oxide. The term, TS-1 is also cited in European Patent Application Nos.267,362 and 190,609.
TS-1 has excellent selection characteristics to specific products due to the use of titanium oxide instead of aluminum oxide. That is, TS-1 has an industrially specific catalytic function in the epoxidation of unsaturated hydrocarbons; hydroxidation of aromatic hydrocarbons; oxidation of saturated hydrocarbons and alcohols; and the hydration of benzenes, phenols and alkanes. Also, TS-1 is used as a catalyst in many other reactions such as a methanation, oxidation and dehydration of aliphatic hydrocarbons containing an oxygen; polymerization of compounds having olefinic or acetylenic bonds; cracking, hydrocracking and isomerization of n-paraffins and naphthenes.
Most synthetic zeolites for such uses are prepared by hydrothermal synthesis at a high temperature (130.degree..about.200.degree. C.) and under high pressure (20.about.80 air pressure). The synthetic zeolite thus prepared is in powder form having a particle size ranging from 0.1 .mu.m to several .mu.m.
A conventional zeolite is difficult to use directly because of this powder form, and therefore several methods for using conventional powdered zeolite have been disclosed. In one such method, the powdered zeolite is blended with another inactive ingredient such as alumina and made into a pellet form for use as an adsorbent in the adsorbing process. In this case, however, it is difficult to properly use the adsorption surface because the reactant's diffusion rate is reduced when the pressure differences in a packed column increase excessively.
Recently, a preparation of a film form of zeolite for use as an effective separating membrane was disclosed. By the method, a thin layer of zeolite is formed onto a support such as Teflon, a filter paper or stainless steel by using a hydrothermal method [Sano et al, J. Mater. Chem., 2, 141 (1992)]. A film form of zeolite with few surface faults such as pinhole or crack is still under study.
A method for mixing a crystalline zeolite with a polyamide fiber, and then spinning the mixture to produce a textile form of zeolite is disclosed in Japanese Patent Laid-Open Publication No. Hei 4-333,639. Also, a method for coating a zeolite onto a ceramic fiber is disclosed in Japanese Patent Laid-Open Publication No. Hei 5-131,139. However, this method is difficult to apply due to its complexity.
As described above, there is difficulty in utilizing the powdered zeolite due to the complexity of its application.